Many electronic devices comprise a display for presenting information to a user.
In particular with mobile devices, it is of importance to limit the power consumption caused by the display, in order to save battery power and to obtain an acceptable stand-by time of the device. This is achieved with various measures.
Some displays can be used for example in two different display modes, namely a full display mode and a partial display mode.
In the full display mode, the entire active area of the display panel is used for a presentation. The user can see the best image quality in this mode, including for example moving images and full colors, etc. The refresh rate of the display panel may be fixed for instance to 60 Hz so that the user cannot see any abnormal visual effects, like a flickering in the image of the display.
In the partial display mode, only a part of the active area of the display panel is used for a presentation. The user can see the basic information in this mode, but the image quality may be lower than in the full display mode, for example by using only eight-color images, etc. Further, the refresh rate of the display panel may be fixed for instance to 30 Hz so that the user cannot see any abnormal visual effects.
The partial display mode results in a lower current consumption than the full display mode. Switching to the partial display mode can thus be used in a mobile device, which is able to provide a high quality presentation to a user in the full display mode, for reducing the total power consumption, and thus for increasing the standby time.
Normally, the refresh rate for a particular display mode is fixed. It has been proposed in addition, however, to reduce the refresh rate in both display modes, whenever the display is in an idle mode, resulting in a further reduction of the current consumption.
If the display is based on the Liquid Crystal Display (LCD) technology, usually a backlight is provided, in order to facilitate the recognition of the presentation on the LCD panel. This backlight can be switched off whenever it is not needed, in order to limit the current consumption. For instance, it may switch off automatically after a predetermined period of time during which the presentation remains unchanged and during which no user input is detected. Further, it may be switched on only in a dark environment. In addition, the intensity of the backlight may be varied inversely proportional to the intensity of ambient light.
The limitation of the current consumption becomes increasingly important as the resolution of the displays of mobile devices increases, for example from a Quarter Quarter Video Graphics Array (QQVGA) having a resolution of 128×160 pixels to a Video Graphics Array (VGA) having a resolution of 480×640 pixels. High resolution displays have a higher current consumption than low resolution displays, resulting in a shorter standby time.